Auxotrophic Actinobacillus pleurpneumoniae grows in multispecies biofilms without the need for nicotinamide-adenine dinucleotide (NAD) supplementation

Shifts in the swine nasal microbiota following Bordetella bronchiseptica challenge in a longitudinal study

Bordetella bronchiseptica is a widespread, highly infectious bacterial pathogen that causes respiratory disease in swine and increases the severity of respiratory infections caused by other viral or bacterial pathogens. However, the impact of B. bronchiseptica infection on the swine respiratory microbiota has not been thoroughly investigated. Here, we aim to assess the influence of B. bronchiseptica infection on the community structure and abundance of members of the swine nasal microbiota. To do so, the nasal microbiota of a non-infected control group and a group infected with B. bronchiseptica (BB group) were characterized prior to B. bronchiseptica strain KM22 challenge (day 0) and on selected days in the weeks following B. bronchiseptica challenge (days 1, 3, 7, 10, 14, 21, 36, and 42). Bordetella bronchiseptica was cultured from nasal samples of the BB group to assess nasal colonization. The results showed that B. bronchiseptica colonization did not persistently affect the nasal bacterial diversity of either of the treatment groups (alpha diversity). However, the bacterial community structures (beta diversity) of the two treatment groups significantly diverged on day 7 when peak colonization levels of B. bronchiseptica were detected. This divergence continued through the last sampling time point. In addition, Pasteurella, Pasteurellaceae (unclassified), Mycoplasma, Actinobacillus, Streptococcus, Escherichia-Shigella, and Prevotellaceae (unclassified) showed increased abundances in the BB group relative to the control group at various time points. This study revealed that B. bronchiseptica colonization can disturb the upper respiratory tract microbiota, and further research is warranted to assess how these disturbances can impact susceptibility to secondary infections by other respiratory pathogens.

The morphology and metabolic changes of Actinobacillus pleuropneumoniae during its growth as a biofilm

Actinobacillus pleuropneumoniae is an important swine respiratory pathogen. Previous studies have suggested that growth as a biofilm is a natural state of A. pleuropneumoniae infection. To understand the survival features involved in the biofilm state, the growth features, morphology and gene expression profiles of planktonic and biofilm A. pleuropneumoniae were compared. A. pleuropneumoniae in biofilms showed reduced viability but maintained the presence of extracellular polymeric substances (EPS) after late log-phase. Under the microscope, bacteria in biofilms formed dense aggregated structures that were connected by abundant EPS, with reduced condensed chromatin. By construction of Δpga and ΔdspB mutants, polymeric β-1,6-linked N-acetylglucosamine and dispersin B were confirmed to be critical for normal biofilm formation. RNA-seq analysis indicated that, compared to their planktonic counterparts, A. pleuropneumoniae in biofilms had an extensively altered transcriptome. Carbohydrate metabolism, energy metabolism and translation were significantly repressed, while fermentation and genes contributing to EPS synthesis and translocation were up-regulated. The regulators Fnr (HlyX) and Fis were found to be up-regulated and their binding motifs were identified in the majority of the differentially expressed genes, suggesting their coordinated global role in regulating biofilm metabolism. By comparing the transcriptome of wild-type biofilm and Δpga, the utilization of oligosaccharides, iron and sulfur and fermentation were found to be important in adhesion and aggregation during biofilm formation. Additionally, when used as inocula, biofilm bacteria showed reduced virulence in mouse, compared with planktonic grown cells. Thus, these results have identified new facets of A. pleuropneumoniae biofilm maintenance and regulation.

Metabolic dissimilarity determines the establishment of cross-feeding interactions in bacteria

The exchange of metabolites among different bacterial genotypes profoundly impacts the structure and function of microbial communities. However, the factors governing the establishment of these cross-feeding interactions remain poorly understood. While shared physiological features may facilitate interactions among more closely related individuals, a lower relatedness should reduce competition and thus increase the potential for synergistic interactions. Here, we investigate how the relationship between a metabolite donor and recipient affects the propensity of strains to engage in unidirectional cross-feeding interactions. For this, we performed pairwise cocultivation experiments between four auxotrophic recipients and 25 species of potential amino acid donors. Auxotrophic recipients grew in the vast majority of pairs tested (63%), suggesting metabolic cross-feeding interactions are readily established. Strikingly, both the phylogenetic distance between donor and recipient and the dissimilarity of their metabolic networks were positively associated with the growth of auxotrophic recipients. Analyzing the co-growth of species from a gut microbial community in silico also revealed that recipient genotypes benefitted more from interacting with metabolically dissimilar partners, thus corroborating the empirical results. Together, our work identifies the metabolic dissimilarity between bacterial genotypes as a key factor determining the establishment of metabolic cross-feeding interactions in microbial communities.

Actinobacillus pleuropneumoniae Surviving on Environmental Multi-Species Biofilms in Swine Farms

Actinobacillus pleuropneumoniae is the etiologic agent of porcine contagious pleuropneumonia, an important respiratory disease for the pig industry. A. pleuropneumoniae has traditionally been considered an obligate pig pathogen. However, its presence in the environment is starting to be known. Here, we report the A. pleuropneumoniae surviving in biofilms in samples of drinking water of swine farms from Mexico. Fourteen farms were studied. Twenty drinking water samples were positive to A. pleuropneumoniae distributed on three different farms. The bacteria in the drinking water samples showed the ability to form biofilms in vitro. Likewise, A. pleuropneumoniae biofilm formation in situ was observed on farm drinkers, where the biofilm formation was in the presence of other bacteria such as Escherichia coli, Stenotrophomonas maltophilia, and Acinetobacter schindleri. Our data suggest that A. pleuropneumoniae can inhabit aquatic environments using multi-species biofilms as a strategy to survive outside of their host.

Bacterial biofilm-derived antigens: a new strategy for vaccine development against infectious diseases

INTRODUCTION

Microorganisms can develop into a social organization known as biofilms and these communities can be found in virtually all types of environment on earth. In biofilms, cells grow as multicellular communities held together by a self-produced extracellular matrix. Living within a biofilm allows for the emergence of specific properties for these cells that their planktonic counterparts do not have. Furthermore, biofilms are the cause of several infectious diseases and are frequently inhabited by multi-species. These interactions between microbial species are often critical for the biofilm process. Despite the importance of biofilms in disease, vaccine antigens are typically prepared from bacteria grown as planktonic cells under laboratory conditions. Vaccines based on planktonic bacteria may not provide optimal protection against biofilm-driven infections.

AREAS COVERED

In this review, we will present an overview of biofilm formation, what controls this mode of growth, and recent vaccine development targeting biofilms.

EXPERT OPINION

Previous and ongoing research provides evidence that vaccine formulation with antigens derived from biofilms is a promising approach to prevent infectious diseases and can enhance the protective efficacy of existing vaccines. Therefore, research focusing on the identification of biofilm-derived antigens merits further investigations.

Growth effects in oregano plants (Origanum vulgare L.) assessment through inoculation of bacteria isolated from crop fields located on desert soils

Bacteria can establish beneficial interactions with plants by acting as growth promoters and enhancing stress tolerance during plant interactions. Likewise, bacteria can develop multispecies communities where multiple interactions are possible. In this work, we assessed the physiological effects of three bacteria isolated from an arid environment (Bacillus niacini, Bacillus megaterium, and Moraxella osloensis) applied as single species or as a consortium on oregano (Origanum vulgare L.) plants. Moreover, we assessed the quorum-sensing (QS) signaling activity to determine the molecular communication between plant-growth-promoting bacteria. The plant inoculation with B. megaterium showed a positive effect on morphometric and physiologic parameters. However, no synergistic effects were observed when a bacterial consortium was inoculated. Likewise, activation of QS signaling in biofilm assays was observed only for interspecies interaction within the Bacillus genus, not for either interaction with M. osloensis. These results suggest a neutral or antagonistic interaction for interspecific bacterial biofilm establishment, as well as for the interaction with oregano plants when bacteria were inoculated in a consortium. In conclusion, we were able to determine that the bacterial interactions are not always positive or synergistic, but they also might be neutral or antagonistic.

Comparison of metabolic adaptation and biofilm formation of Actinobacillus pleuropneumoniae field isolates from the upper and lower respiratory tract of swine with respiratory disease

Most outbreaks of disease due to infection with Actinobacillus (A.) pleuropneumoniae are caused by pigs already pre-colonised in tonsillar tissue, where the pathogen is protected from exposure to antibiotic substances administered for treatment. As it has been shown recently under experimental conditions, A. pleuropneumoniae displays host tissue-specific metabolic adaptation. In this study, pairs of A. pleuropneumoniae field isolates were recovered from lung as well as from tonsillar and nasal tissue from 20 pigs suffering from acute clinical signs of pleuropneumonia and showing characteristic pathological lung alterations. Metabolic adaptation to the porcine lower and upper respiratory tract of 32 A. pleuropneumoniae serotype 2 field isolates was examined using Fourier transform infrared (FTIR) spectroscopy as a high resolution metabolic fingerprinting method. All strains showed metabolic adaptations to organ tissue reflected by hierarchical cluster analysis of FTIR spectra similar to those previously observed under experimental conditions. Notably, differences in antimicrobial resistance patterns and minimal inhibitory concentrations of isolates from different tissues in the same animal, but not in biofilm production capability in a microtiter plate assay were found. Overall, biofilm formation was observed for 71 % of the isolates, confirming that A. pleuropneumoniae field isolates are generally able to form biofilms, although rather in a serotype-specific than in an organ-specific manner. A. pleuropneumoniae serotype 6 isolates formed significantly more biofilm than the other serotypes. Furthermore, biofilm production was negatively correlated to the lung lesion scores and tonsillar isolates tended to be more susceptible to antimicrobial substances with high bioavailability than lung isolates.

Identification of genes regulated by the two-component system response regulator NarP of Actinobacillus pleuropneumoniae via DNA-affinity-purified sequencing

Identifying the direct target genes of response regulators (RRs) of a bacterial two-component system (TCS) is critical to understand the roles of TCS in bacterial environmental adaption and pathogenesis. Actinobacillus pleuropneumoniae is an important respiratory bacterial pathogen that causes considerable economic losses to swine industry worldwide. The targets of A. pleuropneumoniae NarP (nitrate/nitrite RR), which is the cognate RR of the nitrate/nitrite sensor histidine kinase NarQ, are still unknown. In the present study, a DNA-affinity-purified sequencing (DAP-Seq) approach was established. The upstream regions of a total of 131 candidate genes from the genome of A. pleuropneumoniae were co-purified with the activated NarP protein. Electrophoretic mobility shift assay (EMSA) results confirmed the interactions of NarP with the promoter regions of five selected target genes, including dmsA, pgaA, ftpA, cstA and ushA. The EMSA-confirmed target genes were significantly up-regulated in the narP-deleted mutant in the presence of additional nitrate, whilst the transcriptional changes were restored in the complemented strain. The NarP binding motif in the upstream regions of the target genes dmsA and ftpA were further identified and confirmed by EMSA using the truncated binding motif. The NarP binding sites were present in a total of 25.2% of the DNA fragments captured by DAP-Seq. These results demonstrated that the established DAP-Seq method is effective for exploring the direct targets of RRs of bacterial TCSs and that the A. pleuropneumoniae NarP could be a repressor in response to nitrate.

Nanotube-mediated cross-feeding couples the metabolism of interacting bacterial cells

Bacteria frequently engage in cross-feeding interactions that involve an exchange of metabolites with other micro- or macroorganisms. The often obligate nature of these associations, however, hampers manipulative experiments, thus limiting our mechanistic understanding of the ecophysiological consequences that result for the organisms involved. Here we address this issue by taking advantage of a well-characterized experimental model system, in which auxotrophic genotypes of E. coli derive essential amino acids from prototrophic donor cells using intercellular nanotubes. Surprisingly, donor-recipient cocultures revealed that the mere presence of auxotrophic genotypes was sufficient to increase amino acid production levels of several prototrophic donor genotypes. Our work is consistent with a scenario, in which interconnected auxotrophs withdraw amino acids from the cytoplasm of donor cells, which delays feedback inhibition of the corresponding amino acid biosynthetic pathway and, in this way, increases amino acid production levels. Our findings indicate that in newly established mutualistic associations, an intercellular regulation of exchanged metabolites can simply emerge from the architecture of the underlying biosynthetic pathways, rather than requiring the evolution of new regulatory mechanisms.

Incorporation of Actinobacillus pleuropneumoniae in Preformed Biofilms by Escherichia coli Isolated From Drinking Water of Swine Farms

Actinobacillus pleuropneumoniae, the etiological agent of porcine pleuropneumonia, represents one of the most important health problems in the swine industry worldwide and it is included in the porcine respiratory disease complex. One of the bacterial survival strategies is biofilm formation, which are bacterial communities embedded in an extracellular matrix that could be attached to a living or an inert surface. Until recently, A. pleuropneumoniae was considered to be an obligate pathogen. However, recent studies have shown that A. pleuropneumoniae is present in farm drinking water. In this study, the drinking water microbial communities of Aguascalientes (Mexico) swine farms were analyzed, where the most frequent isolated bacterium was Escherichia coli. Biofilm formation was tested in vitro; producing E. coli biofilms under optimal growth conditions; subsequently, A. pleuropneumoniae serotype 1 (strains 4074 and 719) was incorporated to these biofilms. Interaction between both bacteria was evidenced, producing an increase in biofilm formation. Extracellular matrix composition of two-species biofilms was also characterized using fluorescent markers and enzyme treatments. In conclusion, results confirm that A. pleuropneumoniae is capable of integrates into biofilms formed by environmental bacteria, indicative of a possible survival strategy in the environment and a mechanism for disease dispersion.

Actinobacillus pleuropneumoniae biofilms: Role in pathogenicity and potential impact for vaccination development

Actinobacillus pleuropneumoniae is a Gram-negative bacterium that belongs to the family Pasteurellaceae. It is the causative agent of porcine pleuropneumonia, a highly contagious respiratory disease that is responsible for major economic losses in the global pork industry. The disease may present itself as a chronic or an acute infection characterized by severe pathology, including hemorrhage, fibrinous and necrotic lung lesions, and, in the worst cases, rapid death. A. pleuropneumoniae is transmitted via aerosol route, direct contact with infected pigs, and by the farm environment. Many virulence factors associated with this bacterium are well characterized. However, much less is known about the role of biofilm, a sessile mode of growth that may have a critical impact on A. pleuropneumoniae pathogenicity. Here we review the current knowledge on A. pleuropneumoniae biofilm, factors associated with biofilm formation and dispersion, and the impact of biofilm on the pathogenesis A. pleuropneumoniae. We also provide an overview of current vaccination strategies against A. pleuropneumoniae and consider the possible role of biofilms vaccines for controlling the disease.

Effect of Simultaneous Exposure of Pigs to Streptococcus suis Serotypes 2 and 9 on Their Colonization and Transmission, and on Mortality

The distribution of Streptococcus suis serotypes isolated from clinically infected pigs differs between geographical areas, and varies over time. In several European countries, predomination of serotype 2 has changed to serotype 9. We hypothesize a relation, with one serotype affecting the other in colonization and invasion. The aim of this study was to evaluate whether simultaneous exposure of pigs to serotypes 2 and 9 affects colonization and transmission of each type, and mortality. Thirty-six caesarean-derived/colostrum-deprived piglets were randomly assigned to three groups, and there housed pair-wise. At six weeks old, one pig per pair was inoculated with either one (serotype 2 or 9; mono-group) or two serotypes simultaneously (dual-group); the other pig was contact-exposed. Tonsillar and nasal samples were collected within three weeks post inoculation. Bacterial loads in samples were quantified using multiplex real-time polymerase chain reaction (PCR). Transmission rates of the serotypes among pigs were estimated using a mathematical Susceptible-Infectious (SI) model. Bacterial loads and transmission rates did not differ significantly between serotypes. Compared to the mono-group, in the dual-group the average serotype 2 load in tonsillar samples from contact pigs was reduced on days 1 to 4 and on day 6. Simultaneous exposure to the serotypes reduced the mortality hazard 6.3 times (95% C.I.: 2.0–19.8) compared to exposure to serotype 2 only, and increased it 6.6 times (95% C.I.: 1.4–30.9) compared to exposure to serotype 9 only. This study indicates that serotype 2 load and mortality were affected in pigs exposed to these two serotypes.

The Bordetella Bps Polysaccharide Is Required for Biofilm Formation and Enhances Survival in the Lower Respiratory Tract of Swine

Bordetella bronchiseptica is pervasive in swine populations and plays multiple roles in respiratory disease. Additionally, B. bronchiseptica is capable of establishing long-term or chronic infections in swine. Bacterial biofilms are increasingly recognized as important contributors to chronic bacterial infections. Recently the polysaccharide locus bpsABCD has been demonstrated to serve a critical role in the development of mature biofilms formed by the sequenced laboratory strain of B. bronchiseptica We hypothesized that swine isolates would also have the ability to form mature biofilms and the bpsABCD locus would serve a key role in this process. A mutant containing an in-frame deletion of the bpsABCD structural genes was constructed in a wild-type swine isolate and found to be negative for poly-N-acetylglucosamine (PNAG)-like material by immunoblot assay. Further, the bpsABCD locus was found to be required for the development and maintenance of the three-dimensional structures under continuous-flow conditions. To investigate the contribution of the bpsABCD locus to the pathogenesis of B. bronchiseptica in swine, the KM22Δbps mutant was compared to the wild-type swine isolate for the ability to colonize and cause disease in pigs. The bpsABCD locus was found to not be required for persistence in the upper respiratory tract of swine. Additionally, the bpsABCD locus did not affect the development of anti-Bordetella humoral immunity, did not contribute to disease severity, and did not mediate protection from complement-mediated killing. However, the bpsABCD locus was found to enhance survival in the lower respiratory tract of swine.